In recent years, digital voice recording techniques have gradually replaced the traditional methods of analog recording which are typically bulky and difficult to carry out. Digital voice recording apparatus has the benefits of small volume, low consumption of electricity and a large variety of different applications. It is gaining wide popularity in consumer electronic goods such as talking greeting cards, phone answering machines and a variety of talking toys.
When a digital sound recording apparatus is used by an operator to record a sound in a certain environment, there is a high likelihood that background noise exists in that environment which is caused by either electrically operated equipment such as computers, air conditioning units and other office machines or other uncontrollable situations such as passing cars, human voices, etc. This unwanted noise is recorded together with the intended audio signals by the digital recording system and thus deteriorates the quality of the total sound recording.
Eliminating noise in a digital recording system has been of principal concern since the advent of the technology. In analog sound systems, noise is in the form of additive white Gaussian noise which is spectrally constant and benign to a listener; this noise background is considered benign since it is uncorrelated with the audio signal. There are numerous methods of reducing noise and distortion in analog systems, they can often be minimized through stringent design and manufacture of their components.
Noise and distortion in a digital system such as digital sound recording are of a different nature. They can be correlated with the signal, that is, they change according to the signal behavior. A correlated noise seems to increase perceptually at low signal levels and can be quite audible.
Known in the art are various methods of dealing with noise in digital systems. They often require an investigation of the critical band concept and masking curves, i.e. to relate distortion and noise to the human auditory mechanism. The basic idea in suppressing noise lies in "decorrelating" it by reducing it to a low-level noise floor. Nevertheless, the problem of noise in digital systems is not solved since either noise cannot be completely eliminated or the solution to complete eliminating proves to be too expensive.
It is therefore an object of the present invention to provide a method of eliminating background noise in a digital sound recording/playback system such that the quality of the sound can be improved.
It is another object of the present invention to provide a method of eliminating background noise in a digital sound recording/playback system which eliminates background noise in the recording while not significantly increasing the cost of the equipment.